Acoustic beams are used in many applications, including sonar and other underwater acoustic devices, audio transducers, and acoustic control of space, for example architectural acoustics.
In sonar and underwater acoustic devices, the objective can be to map the ocean floor or to detect stationary or moving objects within the water. Additional uses for underwater acoustic devices includes fish finding and fish population estimation, inspection of underwater objects such as boat hulls, piers, and navigation. In many of these applications, it is desirable to utilise an acoustic transducer that is capable of projecting far-field acoustic swath beams. Swath beams are generally considered to be beams that cover a wide angle in one direction and a narrow width in the perpendicular direction.
Known acoustic transducers for projecting swath beams generally comprise an array of active transducer elements that are arranged as either line arrays or alternatively convex cylindrical arrays. Both of these types of acoustic transducers have limitations. For example, the line array acoustic transducers typically have beam power limitations due to their limited width.
As to the convex cylindrical array transducers, these have size constraints in that they cannot generally be made smaller than several wavelengths in diameter relative to the operating frequency due to structural requirements. For example, FIG. 1 shows a cross-sectional end view of an example of a known structure for a convex cylindrical array transducer 10 for producing swath beams. Briefly, the convex cylindrical transducer 10 comprises an array of active transducer elements 12 that are fixed in a convex cylindrical arrangement within a support structure 14. In operation, the transducer elements 12 are driven to project an overall wide-angle swath beam via acoustic aperture 16. The acoustic aperture 16 has a width defined by arrows 20. Typically, the transducer elements 12 have a thickness of about a half wave-length relative to the operating frequency, and this requires a substantial spacing 18 between the front surfaces of the elements. Therefore, the convex cylindrical transducer 10 generally needs to be at least several wavelengths in diameter to operate effectively. This is because arranging the elements 12 into a convex cylinder having a smaller diameter increases the spacing 18 between the elements and this tends to result in prohibitively large response variations within the angle of interest of the swath beam.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.
It is an object of the present invention to provide an improved acoustic transducer for projecting and/or receiving swath beams, or to at least provide the public with a useful choice.